The present invention relates to a blinking detecting device which detects whether or not an eye has blinked during an eye examination with an opthalmological instrument.
During automatic measurements with an opthalmological instrument in which an optical pattern is projected onto the eye and the eye is examined using light beams reflected from the retina, the eye often blinks during which times the opthalmological instrument cannot receive light beams reflected from the retina. If the light beams reflected from the retina are intercepted by the eyelids during the examination, the interception is detected as a signal variation by the detector. Accordingly, the result which should be obtained by analyzing the true signal variation may be subject to a large error. Thus, blinking provides a large problem during these measurements.
In order to detect the blinking, a method has been disclosed in U.S. Pat. No. 3,802,768 in which an analog output signal corresponding to the variations in image formation of the above-described optical pattern is detected and an automatic eye refraction meter for analyzing the signal to calculate the eye refractive power is used to detect the variation rate of the analog signal thereby to detect the start of the blinking.
However, the conventional method is still disadvantageous in the following points. If the pupil diameter is small, the analog signal has a low level, and accordingly, it is difficult to detect the blinking. The method cannot detect the eye closure period during the blinking. If the true variation rate of the analog signal is close to the signal variation rate due to the blinking, it is difficult to distinguish them from each other.
Accordingly, an object of the present invention is to provide a blinking detecting device which can positively detect whether the eye is open or closed and which is not affected by the signal level or signal variations produced by the eye under examination.